Personally I can't imagine anything worse than a turf roof in monsoon conditions even though I have never experienced such weather. In the monsoon, your roof is going to be the most miserable sodden thing, and whatever earth you had on it would quickly displace straight down the water spouts. The only good thing I can think about the turf roof is that when (what's left of) it was drying out, it would cool the structure. So the toboggan must represent a rather lovely thing then; the idea of water splashing about rather than soaking in, the idea of the joy of the monsoon's long awaited arrival. Or maybe just Mme Sarabhai's kids just loved water slides. Certainly it is about an idea of water and it's pleasures, and surely not about the actuality of water on the roof running down the slide and ruining the pool.
But looking at the picture above, and knowing that the division between inside and outside in this building is very flimsy indeed (bamboo screens) brings a bigger fear than mildew and mould and the consequences, joyful or otherwise, of splashing about in the monsoon. Two years ago they found a king cobra under the immigration desk at Ahmedabad International Airport. Cobras can get anywhere and with the monsoon cobras pop up everywhere; mad cobras, driven mad by the weather just like the humans. I think Le Corbusier would have thought I was a complete ninny for worrying about mad cobras under my day bed, but I tell you that's all I can think of (apart from tobogganing in snow, and drips on my head) in such conditions as I imagine within the Villa Sarabhai each June.
The building is presently full of modern art. I hope they are oil paintings rather than drawings. It would be most distressing to have your Picasso drawing turn pea green in such open ventilation. I also suspect that Mme Sarabhai and family have long since decamped to more five star accommodation in another part of their enormous compound, where closets and air conditioning abound.
Such is often the way with great architecture; it's thoroughly impractical. However, when you think about it, it only came down to a simple choice. If LC had plumped for the usual solution of a house on piloti, and not gone all barefoot in the park, the snakes would have stayed on the ground where they belong, and the elevated house would catch the breeze. Funnily enough that's exactly what he did with his next commission for a house in India, the Villa Shodan.